Your cartridge was made by Small Arms ammunition Factory Number 2, Footscray. this ammunition was made primarily for the Thompson Submachine gun, of which Australia used quite a few. They may have have some .45 pistols as well - I am not sure. You also find .45’s with the headstamp “MF” which was S.A.A.F. Number 1, Footscray until after WWII, when “M.G.” was dropped and the former S.A.A.F. Factory 2 began using the “M.F.” designation.